There are airbags that restrict the discharge of gas from a vent hole provided to the airbag by having the vent hole covered with a vent hole cover when the airbag is deployed using gas introduced from the inflator. The vicinity of the vent hole is supported by a cover guide member so that the vent hole cover does not become displaced from the vent hole (see, e.g., Patent Document 1).
In accordance with the airbag disclosed in Patent Document 1, the discharge of gas is restricted by the vent hole cover until the airbag is deployed in a shape that can restrain the passenger. When the airbag has deployed until a shape that can restrain the passenger is formed, the thread holding the vent hole cover is severed.
The vent hole cover is released from the thread when the thread is severed, the vent hole cover is pressed from the vent hole to the exterior of the airbag, and gas is released to the exterior from the gap formed between the vent hole cover and the vent hole, whereby the internal pressure of the airbag can be adjusted.
The airbag of Patent Document 1 has a cover guide member that supports the vicinity of the vent hole so that the vent hole cover does not become displaced from the vent hole. However, the cover guide member does not support the area that corresponds to the vent hole (i.e., the area that blocks the vent hole) and it is therefore difficult to provide support so that the area that corresponds to the vent hole does not become displaced (positionally displaced) from the vent hole.
For this reason, it is possible that gas discharges to the exterior from the vent hole before the airbag deploys to a shape that can provide restraint. In view of this possibility, the amount of gas discharged by the inflator must be increased a certain amount in order to adequately deploy the airbag.